Method and Apparatus for Membrane-Based, Two-Stage Gas Production from Solid Biomaterials

ABSTRACT

Embodiments of the present invention preferably relate to a method and apparatus for a two-stage membrane-based production of gas, preferably hydrogen gas or the like, from solid biological materials, preferably organic waste materials or the like, comprising anaerobic hydrolysis and fermentation and photofermentation using microorganisms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/011,121 (U.S. Pat. No. 8,093,041), entitled “Method and Apparatus forMembrane-Based, Two-Stage Gas Production from Solid Biomaterials”, filedon Jan. 23, 2008 which claims priority to U.S. Provisional PatentApplication Ser. No. 60/886,250, entitled “Membrane-BasedBiohydrogenesis for Enhanced Biological Production of Hydrogen FromOrganic Wastes,” filed on Jan. 23, 2007, and the specifications andclaims of both applications are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of contract No.BES-06070175 awarded by the National Science Foundation and of ContractNo. 601660 SU-83248501-0 awarded by the U.S. Environmental ProtectionAgency.

COPYRIGHTED MATERIAL

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The owner has no objection tothe facsimile reproduction by anyone of the patent document or patentdisclosure, as it appears in the Patent and Trademark Office patent fileor records, but otherwise reserves all copyrights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to a two-stage membrane-based apparatusand method for production of gas from biological materials usingfermentative and photosynthetic processes.

2. Description of Related Art

Note that the following discussion refers to a number of publications byauthor(s) and year of publication, and that due to recent publicationdates certain publications are not to be considered as prior artvis-à-vis the present invention. Discussion of such publications hereinis given for more complete background and is not to be construed as anadmission that such publications are prior art for patentabilitydetermination purposes.

Hydrogen (H₂) has been identified as a renewable and pollution-freehigh-efficiency carrier that has the potential to replace thenonrenewable fossil fuels of today. However, currently available H₂production technologies, such as electrolysis or biomass gasification,are energy-intensive and expensive. Many technical challenges relatingto hydrogen's generation, storage, and usage remain to be solved beforeit can be widely adapted for use.

Hydrogen can be produced by thermochemical, electrochemical, orbiological processes. Of the three, biological processes are emerging asmore environment-friendly, less energy-intensive, and sustainable.Recent research suggests that hydrogen produced via biological processesor from biomass, i.e. biohydrogen, is feasible, where the biomass isorganic matter such as chemical feedstock or waste streams, and can besustainable and cost-effective in the latter case. Current research hasidentified three processes as viable for biohydrogen production:biophotolysis by cyanobateria; photofermentation by anoxygenicphototrophic bacteria; and fermentation by anaerobic bacteria. Thefollowing are examples of such hydrogen production technologies.

U.S. Pat. No. 7,083,956 to Paterek, entitled “Method For HydrogenProduction From Organic Wastes Using a Two-Phase Bioreactor System”,issued Aug. 1, 2006, discloses a method for hydrogen production fromorganic wastes and manures using a two-phase bioreactor system withbiodegradable solid being introduced into first stage anaerobicbioreactor utilizing indigenous microflora. The liquid effluent,including fatty acids, is transferred into second stage anaerobicbioreactor, which is not photofermentative. Hydrogen passes throughsemi-permeable fibers of the second stage.

U.S. Pat. No. 6,887,692 to Paterek, entitled “Method and Apparatus ForHydrogen Production From Organic Wastes and Manure,” issued May, 2005,discloses a method and system for hydrogen production in which afeedstock of at least one biodegradable solid is introduced into a firststage anaerobic bioreactor and a liquid effluent formed. A hollow fibermembrane separates liquid phases. The liquid effluent is transferredinto a second stage anaerobic bioreactor having a plurality of hollowsemipermeable fibers having an outer surface coated with a biofilmformed by at least one hydrogenogenic bacteria, which forms hydrogen gaswithin the lumen of the hollow semipermeable fibers. The hydrogen thusproduced is removed from the lumen of the hollow semipermeable fibers.

U.S. Pat. No. 7,138,046 to Roychowdhury, entitled “Process ForProduction Of Hydrogen From Anaerobically Decomposed Organic Materials,”issued Nov. 21, 2006, discloses a process for the production of hydrogenfrom anaerobically decomposed organic materials by applying an electricpotential to anaerobically decomposed organic materials to form hydrogengas.

Anaerobic technology has been proven to be energy-efficient instabilizing organic waste streams. Reports from several laboratorystudies and full-scale projects have documented successful applicationsof this technology in stabilizing liquid waste streams and generatingenergy in the form of gaseous methane. However, large-scale applicationof this technology in stabilizing particulate wastes to produce energyhas been hindered by the poor kinetics of the overall process.Conversion of particulate organic wastes to gaseous methane involvesmultiple steps in series and parallel, diverse groups of microorganisms,and different environments.

The following have been recognized as important stages in the process.In the first stage, acidogenic organisms solubilize particulatesubstrates extracellularly by enzymatic hydrolysis. In the second stage,acidogenic organisms catabolize the products of the first stage intovolatile organic acids, carbon dioxide, and hydrogen. In the next stage,acetogenic organisms convert the products of the second stage to aceticacid. Finally, methanogenic organisms convert the acetic acid to carbondioxide and methane.

Hydrogen is removed by absorption in materials such as Pd and LaNi₅;stripping by boiling or by a recirculating gas such as nitrogen; orevaporation at large surface areas. However, these approaches areexpensive, energy-intensive, or impractical for large-scaleapplications.

Typical gas components in biogas include CH₄, N₂, CO₂, H₂O (vapor) andtrace amounts of NH₃, H₂S, and HCl. Traditional biogas separationprocesses focus on CH₄ enrichment, which is similar to CO₂ separationfrom natural gas. Both adsorption and membrane processes have previouslybeen applied in biogas separation. A hollow fiber membrane separationprocess for natural gas upgrade has been commercialized by Air Liquide(MEDAL-Air Liquid). Palladium and alloy membranes for H₂ separation fromgas mixtures have been extensively studied and documented. The mechanismof H₂ transport through such membranes involves the following series ofsteps: adsorption; dissociation; ionization; diffusion; reassociation;and desorption. Within the metal, H₂ loses its electron to the palladiumstructure and diffuses through the membrane as a proton. At the exitsurface the reverse process occurs. The trace components including NH₃,H₂S, and HCl in biogas could potentially poison the precious metalcomponents in the H₂ separation membrane and significantly reduce themembrane performance and stability. Microporous SiO₂ membranes haveshown high selectivity and permeability for H₂ at close to ambienttemperature.

While recent research has reported on biohydrogen production from liquidorganic substrates in pure and sterile forms, embodiments of the presentinvention preferably comprise an apparatus and method to producehydrogen from solid biological material, such as organic solid wastes(OSWs) or the like. Unlike the inventions mentioned above, embodimentsof the present invention preferably comprise an apparatus and method ofanaerobic hydrolysis and fermentation, or a chemical conversion ofcarbohydrates into alcohols or acids in the absence of oxygen, in tandemwith photofermentation, and comprising a gas-specific membrane.Embodiments of the present invention preferably comprise a single vesseldesign incorporating at least two steps, an anaerobic fermentation stageand a photofermentation stage, and preferably comprise a membrane,preferably a hollow fiber membrane, separating fluid or gaseous phases.Other embodiments of the present invention preferably comprise anapparatus and method comprising biological conversion of acids to a gasand a heat treatment to suppress methanogens.

Embodiments of the present invention preferably comprise a two-stepprocess configuration for hydrogen production, preferably at roomtemperature, from biomaterials with the first step preferably comprisinggenerating H₂ gas or other gases through anaerobic hydrolysis andfermentation and the second step comprising generating additional H₂ gasor other gases through photofermentation of the products of the firststage and stabilizing the waste.

For sustainable H₂ production, substrates should preferably becarbohydrates from renewable sources at sufficient concentrationsrequiring minimum pretreatment, and available throughout the year at lowcost. Materials comprising OSWs meet these requirements, and may beideal feedstocks for biohydrogen production from the standpoint ofpollution prevention, economics, and sustainability. Cellulose,hemicellulose, and lignin are the primary components of plant cells, andare thus the primary components of OSWs such as biomass wastes, foodwastes, and farm wastes. The conversion of cellulose and hemicellulosefirst to glucose and xylose, respectively, and then to hydrogen,therefore, is a rational and sustainable solution to abatement ofpollution, depletion of fossil fuel reserves, and emissions ofgreenhouse gases.

Biohydrogen has recently been produced from liquid organic substrates inpure and sterile forms, but there is a need for producing biohydrogenfrom any kind of biomaterials, including solid biomaterials.Additionally, combining waste stabilization and H₂ production in thismanner conserves limited resources and be a cost-effective andsustainable approach. Cattle manure is currently produced at a rate of2.2×10⁴ kg/yr/cow, which translates to a COD equivalent of 2×101⁴ kg/yr.The current practice of applying the manure to the ground as afertilizer runs in the face of new regulations that prohibit landapplication.

There is currently a need for an optimal process configuration fordevelopment of a dry digestion process, modifying anaerobic technologyto produce hydrogen rather than methane. While methane generation fromwastes is well understood and has been reported upon, embodiments of thepresent invention preferably generate gas by two processes in tandem,which has previously not been accomplished. Even though the viability ofthe two processes has been demonstrated individually, the presentinvention integrates the two for larger scale practical applications.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention preferably comprise a system forproducing a gas preferably comprising a multi-stage reactor preferablycomprising at least one leach-bed reactor, at least one suspended-growthreactor, and a gas-specific membrane system preferably in fluidcommunication with the multi-stage reactor. The suspended-growth reactoris preferably in fluid communication with the leach-bed reactor. Thesuspended-growth reactor preferably comprises a continuous stirred-tankreactor. The multi-stage reactor preferably comprises a plurality oftubes, where the tubes are preferably perforated. The gas-specificmembrane system preferably comprises ruthenium, nickel, alumina, oralumina composite. The gas-specific membrane system preferably comprisesa hydrogen-selective membrane. The suspended-growth reactor preferablycomprises a light source. The suspended-growth reactor preferablyfurther comprises a magnetic stirrer. The leach-bed reactor preferablycomprises a fixed-bed reactor.

Embodiments of the present invention preferably comprise a method forproducing gas preferably comprising the steps of anaerobichydrolysis-fermentation; photofermentation; removing the gas; andmaintaining pH. The anaerobic hydrolysis-fermentation andphotofermentation may occur in tandem. The anaerobichydrolysis-fermentation preferably comprises percolating leachate incross flow mode. The anaerobic hydrolysis-fermentation preferablycomprises anaerobically fermenting leachate preferably at roomtemperature to preferably produce gas (e.g. hydrogen gas), carbondioxide, and fatty acids. The photofermentation preferably comprisesconverting fatty acids to preferably produce gas (e.g. hydrogen), carbondioxide, and organic residue. The anaerobic hydrolysis-fermentation andphotofermentation preferably occur at room temperature. Maintaining pHpreferably comprises monitoring and controlling different pH levels indifferent stages. Hydrogen partial pressure is preferably maintained andproduct inhibition is preferably avoided by preferably rapidly andefficiently separating the gas. Anaerobic hydrolysis-fermentationpreferably occurs in a leach-bed reactor. Photofermentation preferablyoccurs in a suspended-growth reactor stage. Anaerobichydrolysis-fermentation preferably comprises fermenting a biomaterial.The biomaterial is preferably a solid. Anaerobic hydrolysis-fermentationand photofermentation preferably comprise utilizing naturally occurringorganisms in manure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings which are incorporated into and form a part ofthe specification, illustrate one or more embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating one or more preferred embodiments of the invention and arenot to be construed as limiting the invention. In the drawings:

FIG. 1 is a schematic of a reactor illustrating an embodiment of thepresent invention;

FIG. 2 is a computer-generated image of a schematic of the overview ofthe preferred embodiment of the method of the invention;

FIG. 3 is a diagram illustrating the energetics of a sequence ofprocesses of an embodiment of the present invention;

FIG. 4 is a computer-generated image graph of dissolved carbon oxygendemand (COD) over time;

FIG. 5 is a computer-generated image graph of dissolved carbon oxygendemand (COD) (measured) versus dissolved COD (predicted);

FIG. 6 is a computer-generated image graph of a compilation of COD meanprofiles for eight parameters, including biokinetic coefficients andhydrolysis rate constants;

FIG. 7 is a drawing illustrating a conceptual model of a batch system;

FIG. 8 is a computer-generated image graph illustrating comparisons ofdissolved COD production with and without biocide;

FIG. 9 is a graph illustrating average pH in the liquid phase inreactors;

FIG. 10. is a graph illustrating enhancement of hydrolysis by cellulose;

FIG. 11 is a graph illustrating a comparison of three hydrolysis modelsreferencing Reactor 1 where each inset shows measured COD vs. predictedCOD;

FIG. 12 is a graph illustrating a comparison of three hydrolysis modelsreferencing Reactor 2 where each inset shows measured COD vs. predictedCOD;

FIG. 13 is a graph illustrating a comparison of three hydrolysis modelsreferencing Reactor 3, where each inset shows measured COD vs. predictedCOD;

FIG. 14 is a graph illustrating a comparison of three hydrolysis modelsreferencing Reactor 4, where each inset shows measured COD vs. predictedCOD;

FIG. 15 is a graph illustrating a comparison of three hydrolysis modelsreferencing Reactor 5, where each inset shows measured COD vs. predictedCOD;

FIG. 16 is an illustration of overall comparisons of measured COD andpredicted COD of three hydrolysis models;

FIG. 17 is an illustration of a scanning electron microscope (SEM) imageof binary Ru—Ni nanoparticles; and

FIG. 18 is an illustration of an overall X-Ray mapping of nanoparticleswith a core-and-shell structure of the Ru—Ni nanoparticles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Details of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

An embodiment of the present invention preferably comprises a reactorcomprising: hydrogen selective separation membranes that maximizehydrogen production from OSWs; microbial populations and metabolisms ina biological hydrogen production process; a membrane system for hydrogenseparation and purification; a refined model for hydrolysis/acidogenesisintegrated with a logistic growth model for photofermentation toformulate and validate a complete model for biological hydrogenproduction; and optimal parameters and operating conditions to maximizehydrogen production. Acidogenesis comprises a biological reaction wheresimple monomers are converted into volatile fatty acids.

The present invention comprises a reactor for integrating anaerobicfermentation and photofermentation to produce hydrogen from solidorganic wastes. Hydrogen generation by the two processes preferablyoccurs in tandem. Hydrogen partial pressure (e.g. <2,000 Pa) ismaintained by incorporating a hydrogen selective membrane for efficientremoval of hydrogen. Product inhibition is preferably avoided byincorporating a hydrogen selective membrane for efficient removal ofhydrogen. A different pH for the two stages is maintained by two-stagereactor configuration with individual pH control. Substrate inhibitionis avoided by flexibility to adjust recycle rate. High cellconcentration for anaerobic fermentation is preferably maintained by afixed bed reactor for anaerobic fermentation. Low HRT for anaerobicfermentation is preferably maintained by a fixed bed reactor withrecycling. Uniform and optimal light intensity is preferably maintainedby a suspended growth reactor for photofermentation. In a suspendedgrowth reactor the biomass is preferably suspended in the liquid beingtreated.

Abundant and low cost inocula is employed, preferably by utilizingnaturally occurring organisms in cattle manure. The reactor size isminimized preferably by cross-flow configuration, with built-inillumination. The overall cost is minimized preferably by using endproducts as nursery pots and fertilizers, reusing effluent in pulpingdigested manure, and recycling effluent as fertilizer.

Embodiments of the present invention preferably relate to a method andapparatus comprising two-stage membrane-based production of gas,preferably hydrogen gas or other gas, from solid biological materials,preferably organic waste materials or other biomaterials, usingfermentative and photosynthetic processes comprising microorganisms.Embodiments of the present invention preferably comprise a vessel, suchas a reactor or other vessel, integrating a two-stage process comprisinganaerobic hydrolysis and fermentation and photofermentation to producegas, including but not limited to hydrogen gas, preferably from solidbiological organic wastes, while suppressing methanogens and stabilizingwastes, and the second step generates additional hydrogen throughphotofermentation of the products of the first stage, as well asstabilizing the waste.

A support for the biomass preferably comprises a manure matrix. Theanaerobic fermentor, comprising the apparatus for anaerobic hydrolysisand fermentation, preferably comprises a leach-bed configuration, withthe leachate preferably percolating in cross flow mode to maximize thehydrolysis and acidogenesis processes. A leach-bed reactor configurationpreferably comprises an efficient dry digestion process.

The photofermentation reactor preferably comprises a continuousstirred-tank reactor (CSTR) configuration to maximize the lighttransmission for the phototrophic process. Gas, including but notlimited to hydrogen, is preferably selectively harvested from bothstages. Another embodiment of the present invention preferably comprisesa flat panel reactor for larger scale, outdoor application.

An embodiment of the present invention preferably comprises a method ofhydrolysis-acidogenesis in leach-bed reactors for the first stage thatis preferably coupled to a second stage comprising a suspended growthreactor, comprising a logistic growth model for photofermentation in thesecond stage. Methane formation is preferably suppressed in a firststage by inhibiting methanogens, preferably by heat-shocking anaerobicsludge to inhibit methane-forming species, maintaining a low hydrogenpartial pressure preferably by using hydrogen-selective membranes in thehead space, maintaining a low hydraulic detention time, and maintaininga pH less than approximately 5.0. Photofermentation is preferablyaccomplished by maintaining a pH from approximately 6.0 to 7.0.

An embodiment of the present invention preferably comprises a processoverview resulting in combustion of hydrogen to produce water, with anenergy conversion efficiency of hydrogen of approximately 55%, and a netyield of 12 moles of hydrogen, or 3,432 kJ. The process comprisesanaerobic fermentation, where:

C₆O₆H₁₂(glucose)+2H₂O=2CH₃COOH(fatty acid)+4H₂(g)+2CO₂(g)

and photofermentation, where:

2CH₃COOH+4H₂O=8H₂(g)+4CO₂(g)

resulting in:

C₆O₆H₁₂(glucose)+6H₂O=12H₂(g)+6CO₂(g).

An embodiment of the present invention preferably comprises a uniquemembrane that rapidly removes biogases and efficiently separates outhigh-purity hydrogen. Embodiments of the present invention preferablycomprise hydrogen-specific membranes that resolve technical problems inconverting wastes to hydrogen by alleviating process feed-backinhibition, preventing conversion and consumption of hydrogen, andconcentrating and purifying the gas product. Thus, the conversion ofsolid waste into a value-added energy-efficient fuel, as well as nurserypots that can be produced from digested residues, addresses currentwaste-management problems in diverse, economically important industries,including but not limited to the dairy and food industries.

A preferred embodiment of the present invention preferably removeshydrogen gas from the bioreactor preferably by using a uniquehydrogen-selective composite membrane, preferably comprising aluminumoxide as a substrate. Embodiments of the present invention preferablycomprise a separation layer comprising a ruthenium-nickel thin filmacting as a catalyst for hydrogen oxidation. Other embodiments of thepresent invention preferably comprise a microporous silicon dioxidematrix.

FIG. 1 illustrates an embodiment of the present invention comprisingreactor 10. Reactor 10 comprises tube 20, tube 22, and tube 24 disposedconcentrically inside tank 30. Feedstock, preferably comprising wetcattle manure, 40, is placed in annular space 60 between tube 20 andtube 22, both preferably perforated. Leachate 50 percolates from tank 30radially through tube 20, through feedstock 40 and into annular space 60between tubes 22 and 24. Thereafter, leachate 50 overflows into tube 24,where it is isolated from acid producing phase 40, so that optimal pHcan be maintained for each phase. Light source 64 is placed at thecenter of tube 24. This configuration enables dry digestion undercontrolled moisture content. Anaerobic fermentation (hydrolysis andacidogenesis) occurs in annular space 60 between tube 22 and tube 24,producing H₂, CO₂ and dissolved fatty acids. Leachate 50 carries thedissolved volatile acids into the second stage in tube 24, wherephotofermentation takes place with the production of H₂ and CO₂. The twostages are fitted with pH monitors/controllers 66 to maintain optimal pHin each stage. A fraction of the effluent is preferably recycled to thefirst stage. Carbon dioxide in headspace 70 is preferably absorbed (e.g.with 50% KOH traps 68). Mixing in the second stage is preferablyprovided by stirrer (e.g. magnetic stirrer 72). Membranes 74 in the twostages enable hydrogen levels to be maintained at a specified pressure.

Thermodynamically, optimal hydrogen production by anaerobic fermentationwith acetate as the end-product is realized only when hydrogen partialpressure in headspace 70 is maintained less than approximately 2,000 Pa.Accumulation of hydrogen in headspace 70 can cause product inhibition.Efficient removal of hydrogen is efficiently removed from headspace 70for continuous hydrogen production.

Embodiments of the present invention preferably comprise an apparatusfor gas separation, preferably hydrogen-selective membranes, preferablycomprising Ru—Ni/γ-Al₂O₃/α-Al₂O₃ composites, microporous SiO₂composites, and hollow fiber membranes. Biogas generated in thefermentation reaction comprises trace amounts of CH₄, NH₃, HCl, H₂S, sothe hydrogen separation membrane preferably tolerates these trace gascomponents. This requirement excludes the use of palladium and palladiumalloy membranes because these precious metals are prone to attack by theacid gases. Ru— Ni/γ-Al₂O₃/α-Al₂O₃ composite membranes comprise α-Al₂O₃substrates to provide mechanical strength, and comprise γ-Al₂O₃ toprovide a transitional layer between a separation layer and amacroporous substrate. The Ru—Ni/γ-Al₂O₃/γ-Al₂O₃ composite membranespreferably comprise a separation layer of Ru—Ni. A transitional layersignificantly reduces the thickness of the separation layer and enhancespermeability and stability.

Embodiments of the present invention preferably comprise a catalyticmembrane and method for optimum proton generation and rate of diffusion.An embodiment of the present invention comprise Ru—Ni membranescomprising catalytic properties that facilitate characteristic hydrogenoxidation reactions that involve H₂ dissociative adsorption on andpermeation through the Ru—Ni surface with both pure H₂ and gas mixturescomprising trace components in the biogas. Another embodiment of thepresent invention preferably comprises a membrane comprising microporousSiO₂ composite membranes preferably comprising an α-Al₂O₃ substrate toprovide the mechanical strength, γ-Al₂O₃ to provide the transitionallayer between the separation layer and the macroporous substrate, and aseparation layer of microporous SiO₂. A sol-gel technique preferablyprepares a top layer and a transitional layer. Pure H₂ and H₂ gaspreferably permeate the composite membranes.

Another embodiment of the present invention preferably comprises amembrane comprising a commercial hollow fiber membrane preferablycomprising an apparatus for separating biogas, especially forbiohydrogen purification. The molar flow rate FH2 (mole/s) of H₂ throughthe membrane may be described by the transport equationF_(H2)=B_(H)A_(m)(p^(n) _(f)−p^(n) _(p)) where B_(H) is the permeance ofthe membrane, A_(m) is the membrane surface, and (p^(n) _(f)−p^(n) _(p))is the difference in partial pressure between the feed side and thepermeate side. The value of n is a function of membrane pore size andhydrogen transport mechanism.

An embodiment of the present invention comprises an integrated processof hydrogen production from particulate organic wastes includinghydrolysis, acidogenesis, anoxygenic photosynthesis, and separation ofhydrogen from biogases in order to produce biohydrogen.

An embodiment of the present invention is illustrated in FIG. 2.Acidogenic bacteria 88 exist as a biofilm in manure matrix 78. Theparticulate degradable portion of cattle manure is comprised ofhemicellulose 80 and cellulose 82. These two fractions are enzymaticallyhydrolyzed to their soluble hemicellulose 84 and soluble cellulose 86and then degraded by acidogens 88 in first stage 90 at different rates,to produce fatty acids, H₂ and CO₂. The hydrolysis of hemicellulose 80,and of cellulose 82 are surface limiting reactions while the utilizationof soluble hemicellulose 84 and of soluble cellulose 86 by acidogens 88are a two-substrate-single-biomass. The fatty acids in the dissolvedform flow from first stage 90 to second stage 92, where phototrophicbacteria 94 utilize them in the presence of light 96, to produce H₂ andCO₂.

An embodiment of the present invention comprises a downflow leach-bedreactor fed with cattle manure, modified for radial cross flow andutilizing a photosynthetic process and a membrane process. In addition,the present invention accommodates pH variation and speciation ofvolatile acids.

Anaerobic fermentation followed by photofermentation of the products isan optimal process for producing H₂. This two-step configurationproduces H₂ at a practical rate and economic yield with minimal energyneeds, and at the same time, stabilizes wastes. Embodiments of thepresent invention comprise a substrate comprising biomass, and the CO₂produced by this process is climate-neutral. Energetics of this sequenceof processes utilizing glucose as the feedstock and acetate and butyrateas intermediate products are illustrated in FIG. 3.

Embodiments of the present invention comprise producing H₂ byfermentation of organics comprising cultures of Enterobacter, Bacillus,and Clostridium, of which, the latter have been found to yield themaximum yield of 1.6 to 2.36 M H₂/M glucose. Embodiments of the presentinvention comprise viable production of hydrogen using non-sterilefeedstocks, comprising exploiting natural and/or abundant culturesources, such as soil micro flora or excess sludge from wastewatertreatment plants. However, if mixed cultures from these sources are tobe used, activity of hydrogen-consuming organisms (e.g. methanogens)found in those sources should be inhibited. Methods to inhibitmethanogens include pretreatment of cultures and operating the reactorat short hydraulic retention times (e.g. approximately <8 hrs) and lowpH (e.g. approximately 5 to 6.5). Two pretreatment methods reported tobe effective in suppressing methanogens in the seed are acid-treatmentand heat-treatment.

Embodiments of the present invention comprise generating volatile fattyacids by hydrolysis and acidogenesis in a leach-bed reactor at HRT ofapproximately 2 to 3 hrs and at pH approximately <5.5 using naturallyoccurring organisms in cattle manure residues. Embodiments of thepresent invention comprise inhibiting methanogenesis to levels ofmethane in the gas phase comprising less than approximately 1%.Embodiments of the present invention comprise using naturally occurringorganisms comprise Rhodobacter sphaeroides for photofermentation in thesecond stage.

Embodiments of the present invention comprise a method to use cattlemanure residues as feedstock in producing hydrogen through anaerobicfermentation followed by photofermentation. Cellulose, hemicellulose,and lignin are the primary constituents of cattle manure as well as manyother solid biomaterials.

The invention is further described herein. While the preferredembodiment of the invention is directed to production of hydrogen gasfrom solid organic waste materials, the invention is also useful in anyfuel derivation as appropriate using fermentative and photosyntheticmicroorganisms or their byproducts.

Example 1

A mathematical model for the hydrolysis and acidogenesis reactions inanaerobic digestion/fermentation of cattle manure was performed. Theparticulate hydrolysable fraction of cow manure was composed ofcellulose and hemicellulose that were hydrolyzed at different ratesaccording to a surface-limiting reaction. The respective solubleproducts of hydrolysis were utilized by acidogens at different rates,according to a two-substrate, single-biomass model. Batch experimentalresults were used to identify sensitive parameters and to calibrate andvalidate the model. Results predicted by the model agreed well with theexperimentally measured data not used in the calibration process. Thecorrelation coefficient exceeded 0.91. The most significant parameter inthe hydrolysis-acidogenesis phase was the hydrolysis rate constant forthe cellulose fraction.

A two-substrate, single-biomass model was developed for thehydrolysis/acidogenesis phase and was validated using experimental batchdata. A sensitivity analysis of the model parameters was performed. Atwo-phase reactor system was developed for dry digestion of cattlemanure residues, with a leach-bed reactor comprising the first stage anda suspended growth reactor comprising the second stage. Chemical oxygendemand (COD) generation was optimized by enhancing hydrolysis andacidogenesis and minimizing methanogenic activity by maintaining pHbelow 5.5.

During dry digestion of cattle manure residues in a leach-bed reactor,substrate degradation curves exhibited two distinct segments. Thisobserved two-segment profile was due to two components of cattle manure,a readily degradable faction, hemicellulose, and a slowly degradablefraction, cellulose. Different hydrolysis parameters and biokineticparameters were found for the two components. Two enzymatic mechanismswere found: one mediated by native organisms found in manure residuesand the other mediated by either external enzymes or by seed culturesthat were added to the reactor to augment the hydrolysis process.

In the first mechanism, native organisms grew as colonies attached toparticles in the solid matrix. The rate of hydrolysis by these organismswas dependent on the surface area of the particles occupied by theorganisms. When the surfaces of the particles were fully saturated bythe organisms, the rate was first order with respect to biomassconcentration. In the two-substrate, single-biomass model, thehydrolysis step was modeled as a surface-limiting reaction. In thesecond mechanism, an initial concentration-dependent conversion factorwas modeled. Cellulose was hydrolyzed by a family of enzymes, cellulase.Seed cultures were used to augment hydrolysis. The pH remained below 6.0and had no effect on the hydrolysis rate.

Acidogenesis was subsequently modeled. The acidogenic biomass grew onthe soluble products of hydrolysis consisting of a readily degradablecomponent, hemicellulose, and a slowly degradable component, cellulose.The growth of acidogenic biomass was modeled as a single biomass(acidogens) feeding on two non-inhibitory substrates (solublehemicellulose and soluble cellulose) with different biokineticconstants. The model formulation involved hydrolysis process parametersand biokinetic parameters. The parameters were established following acurve-fitting process using experimental data from a batch reactor runwithout any supplement. Experimental data from two batch reactors withvarious doses of heated anaerobic sludge added as a supplement were thenused to validate the model using parameters estimated from anotherreactor.

Batch experiments were conducted in three 600 mL glass bottles(reactors), each in duplicate. Manure samples were gathered at a nearbydairy farm from a pile under the separator that is used to separate themanure from manure slurry resulting from the cleaning of farm houseswith running water. Average age of the samples in the piles was twodays. Equal amounts of manure sample were placed in each of the sixreactors and filled with equal volumes of water. Reactor 1 did notreceive any external supplements. Reactors 2 and 3 were seeded withdifferent amounts of heat-treated anaerobic sludge from a wastewaterplant. Heat treatment was conducted to suppress the growth ofmethanogens.

Table 1 summarizes the initial concentrations of acidogens, particulatehemicellulose, and particulate cellulose per gram of manure. The initialconcentration of acidogen biomass was estimated from data reported inthe literature. Initial concentrations of dissolved COD, which resultedfrom hemicellulose and cellulose after adding water, are also shown inTable 1. The pH remained below 6 throughout the tests. Methanogens havenegligible activity at pH less than 6.0, thus the dominant processesoccurring in the test reactors was hydrolysis and acidogenesis.

All variables are expressed in chemical oxygen demand (COD) basis. Theprobability that the regression coefficient would be as extreme asreported is p, P_(c) is the concentration of cellulose in particulateform (g COD/g manure), P_(h) is the concentration of hemicellulose inparticulate form (g COD/g manure). P_(i) is the concentration ofcomponent i in particulate form (g COD/g manure). P_(i,0) is the initialconcentration of component i in particulate form (g COD/g manure),P_(t,0) is the initial concentration of total components in particulateform (g COD/g manure), S_(c) is the concentration of cellulose indissolved form (g COD/L), S_(h) is the concentration of hemicellulose indissolved form (g COD/L), X is the concentration of acidogenic biomass(g COD/g solids), a is the solubilization rate of enhancer (g COD/gmanure-day), a_(c) is the biomass yield coefficient with cellulose assubstrate (g COD/g COD), a_(h) is the biomass yield coefficient withhemicellulose as substrate (g COD/g COD), C_(e) is the specific CODconversion rate of enhancers (g COD/g enhancer-day), EMR is theenhancer-to-enhancer ratio (g enhancer/g manure), k_(c) is the maximumsoluble substrate utilization rate of cellulose (1/day), k_(h) is themaximum soluble substrate utilization rate of hemicellulose (1/day),k_(d) is the biomass death rate (1/day), K_(1i) is the hydrolysis rateconstant for component i (1/day or g/g biomass-day), K_(1s,i) is thehalf-saturation coefficient for hydrolysis of component i (g COD/g COD),K_(sc) is the half-saturation coefficient for biomass uptake ofcellulose (g COD/L), K_(sh) is the half-saturation coefficient forbiomass uptake of hemicellulose (g COD/L), and MLR is themanure-to-liquid ratio (g manure/L. water). K_(1s,i), K_(1i) arehydrolysis process parameters and k_(c), k_(h), K_(sc), and K_(sh) arebiokinetic parameters.

TABLE 1 Reactor contents Reactor Reactor Reactor Description 1 2 3Amount of wet cattle manure (g) 120 120 120 Moisture content in wetcattle manure (%) 77.5 77.5 77.5 Amount of seed added, dry (g) 0.00 4.857.28 Initial concentration of biomass (g COD/ 0.035 0.035 0.035 gmanure) Initial concentration of hemicellulose 0.42 0.42 0.42 (g COD/gmanure) Initial concentration of cellulose (g COD/ 0.41 0.41 0.41 gmanure) Initial COD concentration which hydrolyzed 0.83 0.87 0.88 fromhemicellulose (g COD/L) Initial COD concentration hydrolyzed from 0.820.84 0.85 cellulose (g COD/L) Total water (L) 0.523 0.528 0.532Seed-to-manure ratio SMR (g/g) 0.00 0.18 0.927 Dry manure-to-liquidratio MLR (g/L) 51.68 51.15 50.90

Yield coefficients for acidogenic growth on soluble hemicellulose andcellulose were established based on studies on similar substrates. Basedon a sensitivity analysis, when the yield was changed by a factor oftwo, the variation in the COD values predicted was less than 10% of themeasured value. Thus, the yield values were set at 0.084 and 0.042 g CODof VSS/g COD, respectively. Specific COD conversion rates, C_(i), weredetermined by fitting predicted COD data to experimentally measured CODdata from Reactor 2. A correlation coefficient >0.95 and p<0.005 wereused as criteria to establish how good the fit was. This process yieldedspecific COD conversion rates of 0.15 g COD/g sludge for hemicelluloseand 0.001 g COD/g sludge for cellulose. The four hydrolysis parameters(K_(1h), K_(1c), K_(1sh), and K_(1sc)) and the four biokineticparameters (k_(h), k_(c), k_(sh), and k_(sc)) determined through curvefitting using measured data from Reactor 1, and validated with thelaboratory data from Reactors 2 and 3 are listed in Table 2. The maximumhydrolysis rates, K₁ were established for the surface-limiting model(1.4. per day for hemicellulose and 0.09 per day for cellulose). Thehydrolysis saturation constants, K_(1s) were established to be 28 gCOD/g COD for hemicellulose and 1.5 g COD/g COD for cellulose. K_(1sh)and K_(1sc) were the least sensitive of the eight parameters.

A new biokinetic model was used:(dS_(c)/dt)_(uptake)=−k_(c)(S_(c)X/(K_(sc)(1+S_(h)/K_(sh)))+S_(c)) MLR.The maximum growth rate of acidogens k_(i) was found to be 0.51 per dayfor soluble hemicellulose and 0.034 per day for soluble cellulose. Thevalues for saturation constant K_(s) were established as 15 g COD/L forhemicellulose and 100 g COD/L for cellulose.

COD values predicted by the model were compared against measuring data.FIG. 4 illustrates model predictions using the parameters found, closelyfollowing the temporal trend in the measured COD data from Reactor 1,which did not receive any supplement. Measured data from Reactors 2 and3 that received seed supplement were used to further validate the model.The two variables that distinguish Reactors 2 and 3 from each other andfrom Reactor 1 are the seed-to-manure ratio and the manure-to-waterratio compiled in Table 4. FIG. 5 shows agreement between the CODpredicted by the model and the measured COD values from the threereactors. The agreement between the predicted and measured COD valueswas statistically significant (p<0.005), individually for the threereactors (with r²=0.980, 0.933, and 0.872, respectively) as well as forthe three reactors together (with overall r²=0.91 at p<0.002).

A sensitivity analysis was conducted to identify the most sensitiveparameters in the hydrolysis-acidogenesis step. Nine COD profiles weregenerated and then combined to generate a mean profile with a spread ofone standard deviation. A compilation of these mean profiles for each ofthe eight parameters is shown in FIG. 6, along with the measured CODdata from Reactor 1. These plots indicate that the maximum hydrolysisrate constant K_(1c) for cellulose to be highly sensitive, followed bythe biokinetic coefficients k_(h) and k_(sh) for hemicellulose, to alesser extent.

A two-substrate, single biomass model integrating hydrolysis andacidogenesis in anaerobic digestion of cattle manure was validated usingbatch experimental data. Hydrolysis was the rate-limiting step in theanaerobic digestion of complex particulate substrates and was used indesigning, monitoring, analyzing, and optimizing the anaerobicgasification process.

TABLE 2 Model parameter output Value at 37° C. Model ParametersHemicellulose Cellulose Maximum rate of hydrolysis, K_(1i) (day⁻¹)  1.4± 0.13 0.09 ± 0.008 Saturation constant for hydrolysis, K_(1s i) 28.0 ±2.52 1.5 ± 0.14 (—) Saturation constant for fermentation, K_(s i) 15.0 ±1.35 100 ± 9.0  (g COD/L) Maximum substrate utilization rate, k_(i)  1.8± 0.16 0.80 ± 0.07  (1/day)

Example 2

First-order, second-order, and surface-limiting reactions in anaerobichydrolysis of cattle manure were evaluated. Laboratory batch experimentswere conducted with cattle manure as the substrate to evaluate the threehydrolysis models and to validate the hydrolysis-acidogenesis model.Enhancement of hydrolysis by enrichment with enzymes was alsoinvestigated. Cellulase was used as an enhancer solely to validate theprocess model. Samples of cattle manure were obtained from a pile ofdairy filtered manure wash. The age of the test samples in the pile was2 days. The tests were conducted in batch mode in 600 mL glass bottles.Five batch reactors (labeled Reactor 1, 2, 3, 4, and 5) were run, eachwith a duplicate. Reactor 1 contained a raw manure sample, topped withwater. Reactors 2 to 5 contained raw manure, enriched with differentamounts of the cellulose enhancer and topped with water. Another set ofexperiments was conducted to verify that active hydrolytic organismswere already present in the manure samples. In these experiments, two600-mL batch reactors (labeled Reactors 6 and 7) were run in duplicate.Both of those reactors were filled with raw manure samples and water;Reactor 7, however, was dosed with a biocide (1.9 g/L HgCl₂) to inhibitbacterial activity.

Three kinetic models were evaluated for suitability in describinganaerobic hydrolysis of particulate wastes. The three hydrolysis modelsevaluated were: a first-order reaction in particulate substrateconcentration model, a second-order reaction in acidogenic biomass andparticulate substrate concentrations model, and a two-parameter,surface-limiting reaction model. Process models incorporating the threehydrolysis reaction models were developed to describe thehydrolysis-acidogenesis phase in the fermentation of cattle manure.

Batch reactors were run with cattle manure as the substrate under fivedifferent conditions to calibrate and validate the process models. Thetwo-parameter, surface-limiting reaction model and the single-parameter,second-order reaction model were found to fit the experimental resultsbetter than the simple first-order reaction model with r² values of0.914, 0.913, and 0.881, respectively. The temporal COD solubilizationcurve consisted of two distinct segments. This is due to two distinctcomponents of cattle manure: a readily hydrolyzable fraction composedprimarily of hemicellulose and a slowly hydrolyzable fraction composedprimarily of cellulose. These two fractions were identified as the majorconstituents of cattle manure, each wet waste. Naturally existingcellulolytic and hemicellulolytic organisms in cattle manure hydrolyzedthe particulate forms of cellulose and hemicellulose contained therein.

The quantities of manure samples, water, cellulase enrichment, andbiocide added to each reactor are shown in Table 3. All the reactorswere placed in a water bath maintained at 37±2° C. Liquid samples fromthe reactors were withdrawn periodically to measure pH using a pHelectrode probe. The samples were filtered with a 0.45 μm membranefilter and the COD of the filtrate was measured following StandardMethods 522D to determine dissolved COD.

TABLE 3 Contents of test reactors. Description Reactor 1 Reactor 2Reactor 3 Reactor 4 Reactor 5 Reactor 6 Reactor 7 Amount of wet cattlemanure (g) 120 120 120 120 120 100 100 Moisture content in wet manure78.7 78.7 78.7 78.7 78.7 77.3 77.3 (%) Amount of cellulase added (g)0.00 0.05 0.10 0.15 0.20 0.00 0.00 Amount of biocide added (g) 0.00 0.000.00 0.00 0.00 0.00 1.00 Water added to reactor (L) 0.40 0.45 0.45 0.450.45 0.43 0.43 Cellulase-to-manure ratio (mg/g) 0.00 2.00 3.90 5.90 7.80NA NA Manure-to-liquid ratio (g/L) 51.68 46.93 46.93 46.93 46.93 42.8342.83

Example 3

A hydrolysis-acidogenesis phase was modeled and was based on thesimplifying assumptions that the particulate hemicellulose and cellulosefractions were hydrolyzed by acidogens; the acidogens grew attached tothe solid matrix, utilizing the dissolved form of hemicellulose andcellulose as substrate; and the enhancers hydrolyzed the particulatehemicellulose and cellulose in proportion to their respective initialconcentrations. The solubilization efficiency of the enhancer,cellulase, was estimated to be 15% through a curve-fitting process. Asensitivity analysis showed that the change in COD production was within1% when the efficiency ranged from 10 to 20%. There was negligiblemethanogenic activity in the reactors. Thus, the only processesoccurring in the reactors were hydrolysis and acidogenesis.

The modeling framework incorporating these assumptions is illustrated inFIG. 7 illustrating a conceptual model of batch system 90 comprisinghydrolysis 1 of particulate hemicellulose 92, hydrolysis 2 ofparticulate cellulose 94, biouptake 3 of soluble hemicellulose 96, andbiouptake 4 of soluble cellulose 98 to acidogen 99. Based on the aboveassumptions, the rate of change of particulate species i (in the formsof hemicellulose 92 and cellulose 94) due to hydrolysis can be expressedas follows for the three hydrolysis reaction models:

The overall rate of the anaerobic process of gasification of particulatewastes by the above scheme is dependent on the rate limiting stepcomprising the hydrolysis step as the rate-limiting step. Hydrolysisreaction models for use in modeling the hydrolysis/acidogenesis step inthe digestion of cattle manure are:

First-order reaction model:

dP _(i) /dt=−K _(1i)(P _(i))−α(P _(i,0) /P _(t,0))

Second-order reaction model:

dP _(i) /dt=−K _(1i)(P _(i))(X)−α(P _(i,0) /P _(t,0))

Surface-limiting reaction model (Contois kinetic model):

dP _(i) /dt=˜K _(1i)(Pi/X/(K _(1si) +P _(i) /X))(X)−α(P _(i,0) /P_(t,0))

In the above equations, the second term on the right-hand siderepresents the enhancement of hydrolysis by the cellulose enhancerwhere, α is the solubilization rate of the enhancer. While this term waszero for Reactor 1, for Reactors 2 to 5, α is expressed as

α=C _(e) EMR

where C_(e) is the specific COD conversion rate of the enhancer (g COD/genhancer-day) and EMR is the enhancer-to-manure ratio (grams enhancer/gmanure). The specific COD conversion rate of cellulase was obtained fromthe supplier as 2.074 g COD/g cellulase-day.

Regardless of the hydrolysis reaction model, the utilization rates ofdissolved hemicellulose and cellulose by the acidogenic biomass can beexpressed as follows according to the two-substrate—one-biomass model:

Uptake rate of hemicellulose by acidogens:

(dS _(h) /dt)_(u) =−k _(h)(S _(h) X/(K _(sh)(1+S _(c) /K _(sc)))+S_(h))MLR

Uptake rate of cellulose by acidogens:

(dS _(c) /dt)_(u) =−k _(c)(S _(c) X/(K _(sc)(1+S _(h) /K _(sh)))+S_(c))MLR

Therefore, the net rate of change of dissolved species (i=hemicelluloseor cellulose) in the reactor is:

(dS _(i) /dt)=−(dP _(i) /dt)MLR+(dS _(i) /dt)_(u)

Thus, the rate of change of dissolved COD in the reactor is:

${{\left( {C\; O\; D} \right)}/{t}} = {\sum\limits_{i = c}^{i = h}\left( {{S_{i}}/{t}} \right)}$

The rate of growth of acidogenic biomass can be expressed as:

${{X}/{t}} = {{\sum\limits_{i = c}^{i = h}\left\lbrack {\left( {{S_{i}}/{t}} \right)a_{i}} \right\rbrack} - {k_{d}X}}$

where a_(i) is the yield coefficient [−]; and k_(d) is the death rate[1/day].

The model equations contain up to four hydrolysis process parameters(K_(1h) and K_(1sh) for hemicellulose and K_(1c) and K_(1sc) forcellulose) and four biological process parameters (k_(h) and K_(sh) forhemicellulose and k_(c) and K_(sc) for cellulose). Since theseparameters were not measured through independent experiments, acurve-fitting process was used to estimate them. Measured COD data fromReactor 1 was used in the curve-fitting process to estimate the eightparameters, which were then validated using measured COD data fromReactors 2, 3, 4, and 5. The model equations were solved using a dynamicsimulation program to generate the COD profile as a function of time.

The literature was surveyed to determine yield coefficients foracidogenic growth on soluble forms of hemicellulose (a_(h)) andcellulose (a_(c)). Since the substrates, experimental conditions, andthe data analysis methods varied from study to study, it was notpossible to reconcile and corroborate those values. Typical yieldcoefficients ranged as follows: 0.026 g COD of VSS/g COD for cattlemanure wastewater, where VSS is Volatile Suspended Solids; 0.047 g CODof VSS/g COD for amino adds and sugars; 0.057 g COD of VSS/g COD foractivated sludge; 0.051 g COD of VSS/g COD for molasses wastewater; and0.100 g COD of VSS/g COD for with amino acid, sugars, and fatty acid.When comparing the three hydrolysis models, absolute values for theyield coefficients were not established; the same values were used forthe three models, but of appropriate magnitude. The following valueswere used for the yield coefficients: 0.084 and 0.042 g COD of VSS/gCOD, for a_(h) and a_(c), respectively.

Example 4

Modeling assumptions were verified and model parameters were estimated,calibrated, and validated. FIG. 8 is an illustration of the impact ofthe biocide dose on dissolved COD production in Reactors 6 and 7. InReactor 6, which was not dosed with the biocide, COD productioncontinued to increase with time while COD production in Reactor 7, whichwas dosed with the biocide, was significantly lower. The slight increasein COD production in Reactor 7 was due to abiotic processes orinadequate biocide dosage. The production of dissolved COD was primarilydue to active hydrolytic organisms naturally present in cattle manure.

FIG. 9 illustrates that the pH in all the reactors remained below 5.5.Methanogenic activity was negligible in this pH range and the onlyprocesses that occurred in the reactors were hydrolysis andacidogenesis.

FIG. 10 is an illustration of the enhancement of the hydrolysis processas reflected by the increase in COD generation due to increasing dosesof cellulase as the enhancer. COD generation increased 25 to 30% whenthe cellulase-to manure ratio increased from 2 mg/g to 3.9 mg/g.However, further increase of cellulose-to-manure ratio up to 7.8 mg/gdid not result in any increase in COD release due to saturation, due tomass transfer limitations in the hydrolysis step in thissurface-limiting model.

The best-fit values for the eight parameters were found by acurve-fitting process to match the COD data measured in Reactor 1 thatdid not receive any enhancers. The best-fit parameters found for thethree hydrolysis models are compiled in Table 4. The hydrolysisparameters are different for the three models as the underlyingmechanisms are different. In the case of the biological parameters, theestimated k_(i) values are comparable for the three models as expected;while the K_(si) values are comparable for the first-order andsecond-order models, the corresponding values for the surface-limitingmodel are an order of magnitude higher.

TABLE 4 Best-fit values of model parameters. First-order Second-orderSurface limiting Parameter reaction model reaction model reaction modelFor hemicellulose: K_(1h) (day⁻¹) 0.05 ± 0.006 1.2 ± 0.104 1.4 ± 0.12K_(1sh) (—) — — 28.0 ± 2.0  K_(h) (day⁻¹) 1.0 ± 0.12 0.9 ± 0.078 1.8 ±0.16 K_(sh) (g COD/L) 2.2 ± 0.26 2.5 ± 0.22  15.0 ± 1.29  For cellulose:K_(1c) (day⁻¹) 0.019 ± 2.28  0.28 ± 0.024  0.09 ± 0.008 K_(1sc) (—) — —1.5 ± 0.13 K_(c) (day⁻¹) 0.75 ± 0.09  0.5 ± 0.044 0.8 ± 0.07 K_(sc) (gCOD/L) 75.0 ± 9.0  55.0 ± 4.8   100.0 ± 8.6  

The parameters found through curve-fitting were further validated withCOD data from Reactors 2, 3, 4, and 5 that received various doses of theenhancer. The COD profiles predicted by the three models for Reactors 2,3, 4, and 5 agreed with the measured data as summarized in Table 5. Theoverall fit between COD measured experimentally and the COD predicted bythe process model incorporating the three hydrolysis models was good(r²>0.85 for 120 data points, with the probability of the correlation,p<0.001). This model was valid and the observed two-segment COD profileswere due to the two components in cattle manure, i.e. hemicellulose andcellulose.

TABLE 5 Quality of Prediction of the three models. Model Reactor 1Reactor 2 Reactor 3 Reactor 4 Reactor 5 Overall First-order reaction R²0.932 0.851 0.925 0.903 0.894 0.881 (data points = 12) F 137.28 56.93122.88 93.46 83.95 427.48 p <0.001 <0.001 <0.001 <0.001 <0.001 <0.001Second-order reaction R² 0.97 0.903 0.938 0.935 0.913 0.913 (data points= 12) F 324.74 93.56 151.11 143.96 113.08 607.03 p <0.001 <0.000 <0.001<0.001 <0.001 <0.001 Third-order reaction R² 0.992 0.921 0.932 0.9370.911 0.914 (data points = 12) F 1187.74 115.65 137.27 149.68 102.09619.77 p <0.001 <0.000 <0.001 <0.001 <0.001 <0.001

The COD profiles predicted using the three hydrolysis reaction modelswere compared against the measured COD data for Reactors 1 to 5 in FIGS.11 to 15. Overall, the surface-limiting reaction and the second-orderreaction models fitted the measured data better than the first-orderreaction model as shown by the line of perfect fit in FIG. 16. The trendand the closeness of fit of both the first-order and second-orderreaction models deteriorated with time, while the trend and the fit ofthe surface-limiting reaction model was consistent throughout the fullrange of the tests. The substrate-to-microorganism ratio, P_(i)/X, was alimiting factor in the hydrolysis of particulate substrates, rather thanthe remaining substrate concentration P_(i) as modeled by thefirst-order reaction model.

As P_(i) decreased with time, soluble COD and X increased with time, andthe ratio P_(i)/X decreased. By incorporating this limitation, thesurface limiting model predicted the COD better than the other twomodels. This is further corroborated by the fact that the COD generationdid not increase in proportion to the enhancer dose.

The three hydrolysis models predicted COD generation reasonably well.The single-parameter, second-order model was more realistic than thefirst-order reaction model and easy to apply. The surface-limitingreaction model fitted the data with a slightly better quality of fitover the range tested and involved two parameters establishedexperimentally.

Example 5

Studies on anaerobic hydrolysis/acidogenesis of cattle manure toformulate, calibrate, and validate a new mechanistic model for the twoprocesses were conducted. Native organisms in cattle manure residueswere adequate to hydrolyze the particulate organics and to convert thesolublized organics into fatty acids. The pH in all reactors remainedbelow 5.5 under multiple combinations of manure-to-liquid ratios, andCH₄ content of the gas phase was less than 1%. Two additional similarreactors were run with a biocide and confirmed that the COD and volatilefatty acid (VFA) productions were due to the microbially mediatedhydrolysis and acidogenesis. Advective and diffusive transport of thedissolved components was incorporated for application to down-flowlead-bed reactors. Experimental results from two leach-bed reactors fedwith cattle manure residues at different bed porosities and recyclerates were gathered.

Example 6

Membrane processes are implemented for hydrogen fuel cell and hydrogenseparation. Binary Ru—Ni thin films are synthesized to act as novel fuelcell catalysts for hydrogen oxidation. A flash pyrolysis process isdeveloped to deposit Ru—Ni nanoparticles with a core-and-shellstructure. Hydrogen oxidation and permeation properties areinvestigated. The Ru—Ni nanoparticles are deposited on the surface of asol-gel derived mesoporous γ-Al₂O₃ layer as the hydrogen selectiveseparation membrane. The inorganic membranes have sufficiently largeseparation factors for hydrogen and significantly high resistances formembrane fouling.

Binary Ru—Ni thin films are synthesized as novel fuel cell catalysts forhydrogen oxidation and for membrane processes for hydrogen fuel cell andhydrogen separation. Ru—Ni nanoparticles with core-and-shell structurewere deposited by a flash pyrolysis process. A SEM image of the binaryRu—Ni nanoparticles is shown in FIG. 17, and the X-Ray mapping of asingle Ru—Ni nanoparticle is shown in FIG. 18.

Example 7

Key microbial groups are tracked by monitoring their populations as wellas their metabolism. Microbial populations are tracked by combiningculture-based detection methods with molecular-based detection.Populations which are metabolically useful (e.g. spore-formerspotentially involved in hydrogen production) as well as pathogensharbored in the feedstock manure (e.g. fecal coliforms and subsets offecal coliforms such as E. coli 0157) are monitored. A polymerase chainreaction (PCR) is employed to detect pathogenic bacteria, and PCR isused to track other groups of interest. To track the spore-formers inthe sample (many of which produce hydrogen anaerobically), a sporecortex lytic enzyme gene is utilized, which is conserved among manyClostridium and Bacillus species using PCR primers. The culture-basedassay for spore-formers involves pasteurization of the sample, thenplating on non-selective medium grown under anaerobic conditions.Organisms that harbor the hydrogenase enzyme are monitored. For example,the hydrogenase gene in one of the sulfate-reducing bacteria produceshydrogen, and is sequenced; PCR primers track this common Ni—Fe type ofhydrogenase. Indicator pathogens are enumerated using the membrane fecalcoliform standard method, and representative pathogens such as E. coliare PCR-amplified utilizing primers specific for the attaching andeffacing locus (eaeA) gene. Genetic characterization and manipulation isperformed. Bacteria which play key roles in the bioconversion processand genetically characterize appropriate genes by, for example,sequencing PCR products of hydrogenase as well those involved inbutyrate production are isolated. Genetically manipulating appropriateisolates in order to knock out genes that divert electron flow toproducts such as butyrate instead of hydrogen is accomplished.Site-directed mutagenesis is used. Gene knock-out mutants are tested inbioreactor studies to document changes in H₂ production efficiency.

Example 8

Performance is characterized and tested. The reactor is operated at 30°C. in an environmental chamber. The photofermentation occurs underillumination of a 200 W/m² tungsten lamp. A pH controller is used tomaintain the optimal pH for the two stages. Liquid samples collectedfrom the two stages are analyzed for volatile acids, using gaschromatograph with FID; for optical density, using a spectrophotometer;and for COD, following standard methods. The gas production rate fromeach stage is measured using water columns. Gas samples are analyzed bygas chromatograph fitted with thermal conductivity detector. Theoperating parameter is the recirculation rate. Experiments are conductedunder steady and cyclic illumination.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverin the appended claims all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above and/or in the attachments, and of thecorresponding application(s), are hereby incorporated by reference.

1. A method for producing gas from a biomaterial comprising the stepsof: fermenting the biomaterial using anaerobic hydrolysis-fermentation;photofermentating; removing the gas; and maintaining a pH during atleast one stage of the method.
 2. The method of claim 1 wherein theanaerobic hydrolysis-fermentation and photofermentating occur in tandem.3. The method of claim 1 wherein the anaerobic hydrolysis-fermentationcomprises percolating leachate in a cross-flow mode.
 4. The method ofclaim 1 wherein the anaerobic hydrolysis-fermentation comprisesanaerobically fermenting leachate to produce a mixture comprisinghydrogen gas, carbon dioxide, and fatty acids.
 5. The method of claim 1wherein the photofermentating comprises converting fatty acids toproduce a mixture comprising hydrogen, carbon dioxide, and organicresidue.
 6. The method of claim 1 wherein the anaerobichydrolysis-fermentation and photofermentating occur at room temperature.7. The method of claim 1 wherein maintaining the pH comprises monitoringand controlling different pH levels in different stages.
 8. The methodof claim 1 further comprising maintaining hydrogen partial pressure andavoiding product inhibition by rapidly and efficiently separating thegas.
 9. The method of claim 1 wherein the anaerobichydrolysis-fermentation occurs in a leach-bed reactor.
 10. The method ofclaim 1 wherein the photofermentating occurs in a suspended-growthreactor stage.
 11. The method of claim 1 wherein the biomaterial is asolid.
 12. The method of claim 1 wherein the anaerobichydrolysis-fermentation and photofermentating comprise utilizingnaturally occurring organisms.
 13. The method of claim 12 wherein thenaturally occurring organisms occur in manure.
 14. The method of claim 1wherein the anaerobic hydrolysis-fermentation and the photofermentatingtake place in a single vessel.
 15. The method of claim 14 wherein thesingle vessel comprises a multi-stage reactor comprising at least oneleach-bed reactor and at least one suspended-growth reactor, thesuspended-growth reactor in fluid communication with the leach-bedreactor.
 16. The method of claim 15 wherein the single vessel comprisesa gas-specific membrane system disposed above the leach-bed reactor andthe suspended-growth reactor in fluid communication with the multi-stagereactor.
 17. The method of claim 15 wherein the single vessel comprisesa plurality of tubes, wherein a portion of the tubes divide theleach-bed reactor from the suspended-growth reactor within the singlevessel.
 18. The method of claim 17 wherein the single vessel comprisesan annular space between the tubes dividing the leach-bed reactor fromthe suspended-growth reactor.